engleski

Characterization of Pectin Powder Obtained by Different Extraction Methods from Tomato Peel

Processing of tomato fruits into various products (tomato juice, paste, purée, ketchup, sauce and salsa) by food industries generate significant quantity of biodegradable material. Recycling the tomato peels to complex colloidal polymeric carbohydrate pectin was the main target of this study. Pectins are widely used in food industry for a various purpose such as a gelling agent, thickener, texturiser, emulsifier and stabilizer. In order to get better yields, purity and functional properties in shorter time, two different extraction methods, e.g. classical (refluxing) and ultrasonic bath were used in the study. The extraction of dried tomato peels, under reflux in a condensation system, was performed at 60 and 80 °C using ammonium oxalate/oxalic acid as extracting solvent, at time of 24 h in the first step and then subsequently with a fresh volume of extracting solvent during 12 h in the second step. Ultrasonic bath extraction with the same solvent was carried out at frequency of 30 kHz, temperature of 60 and 80 °C, and sonication time of 15, 30, 45, 60 and 90 min. A preliminary characterization of pectins was performed by titrimetric (methoxyl and anhydrouronic acid content, and degree of esterification), gravimetric (calcium pectate) and spectrophotometric (D-galacturonic acid) methods in order to investigate the influence of different extraction methods as well as extraction conditions on the chemical composition of the extracts. The colour of sample was determined as Hunter a, b and L values using Hunter colorimeter. The results obtained for ultrasonic bath extraction showed that yield, methoxyl (MeO) and anhydrouronic acid (AUA) contents and degree of esterification (DE) varied significantly (p<0.05) with the various extraction temperatures used. As the extraction temperature increased from 60 to 80 °C, the yield of pectin increased too, from 15.2 to 17.2 % and 18.1 to 19.7 %, respectively, but MeO and AUA contents and DE decreased. An increase of time had no significant effect on pectin yield as well as MeO and AUA content and DE. The results of pectin quality parameters confirm that both extraction procedures are efficient. The main disadvantage of refluxing extraction is longer extraction time. The pectin yield of 15.1 and 15.2 % was obtained at extraction time of 24 h (reflux) and 15 min (ultrasonic bath), respectively. Obviously, the ultrasonic bath extraction can be used as excellent method for pectin isolation from tomato by-products. The utilization of tomato peels for production of pectin will solve the problems of agricultural waste disposal, and pectin can be used as functional food or as additive in different food processing industries, too.

pectin characterization; pectin extraction; tomato waste

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